It's odd. When I first saw the end cutscene, I didn't really get why they would alter the lead up and end note of Dante and Vergil talking. Now though...Vergil's voice gets quiet, raspy when talking about Nero and after Dante's jackpot, but more relaxed and natural while him and Dante were quipping in the midst of their fights.
It's subtle, but I think it's a nice way to convey how V's humanity (and subsequent character development) carried over to the current Vergil without overstating the point. It makes him uncomfortable to be ashamed...to be vulnerable and honest about how those people he's let down and the childhood he never had.
Fighting though is different. There's less pretense. Both Vergil and Dante (for entirely different reasons) spent their lives turning their martial prowess into an artform. For Dante, it's an escape. A moment where he's not dwelling on how he doesn't truly belong in either the demonic or human worlds. For Vergil...well, it's comfortable version of their lifelong antagonistic tendencies. Less fratricide and more sibling rivalry. A chance to be the kids they never were.
I appreciate that. It's such a minor thing, but they put it in anyway.
Me before playing the Vergil DLC: "I don't see what's so nightmarish about facing Dante while he's using Royal Guard." Me while playing the Vergil DLC: "Okay let's NOT use Mirage Blades..."
5:46 Man, this part was one of the best DMC gameplay moment i ever seen. Both Dante and Vergil went Sin DT and unleash their strongest move. Judgement and Judgment Cut End
Nero: "We didn't even fight, dad"